Twin gestation is often a hazardous pregnancy and especially the monochorionic twin pregnancy significantly contributes to fetal morbidity and mortality. Among the serious complications with twins, the twin-twin transfusion syndrome complicates 5-35% of monozygotic twin pregnancies with monochorionic placentation. Acardiac twinning, earlier known as chorioangiopagus parasiticus, is the most extreme manifestation of this condition. An acardiac twin is a rare complication of multifetal pregnancy, in the literature reported at an incidence of 1% of monochorionic twin pregnancies, i.e. 1 of 35,000 pregnancies. In the following paper we review the literature on the subject and report 6 cases, 5 twins and 1 triplet, that were diagnosed at our department during the period of 1993-1997 and treated conservatively. Only 1 child survived.